The present invention relates to support assemblies for aboveground or elevated pipelines, and more particularly, to support assemblies that allow relative movement between the pipeline and the ground to provide for normal thermal expansion and contraction in the pipeline and apparatus for preventing substantial damage to the pipeline and the support assembly upon occurrence of large, relative movements between the pipeline and the support assembly caused by seismic disturbances.
The most economical means for transporting crude oil or other petroleum products through Arctic regions is a pipeline. Normally such pipelines are subterranean, that is they are installed in back filled trenches that interconnect one or more pumping stations between a well and a shipping terminal or refinery. Through certain Arctic regions, however, a subterranean pipeline is not feasible as the permafrost that constitutes the soil will, under certain temperature conditions, melt and not provide support for the buried pipeline, thus allowing the pipeline to more or sag within the ground and potentially causing damage to the pipeline. The solution to this problem has been to place portions of the pipeline above the ground in Arctic regions.
Not only are pipelines generally not supported above the ground because of the additional cost involved in constructing an elevated pipeline, but Arctic conditions, especially those that exist between the North Slope in Alaska and the Southern coast of Alaska, present problems that have heretofore been unencountered in the construction of a pipeline. First of all, the support members or pilings must generally be oriented perpendicularly to the ground plane, that is vertically, so as to achieve maximum strength with minimum structure and cost. The topography over which the pipeline traverses dictates that the pipeline at any given location of a vertical support member will not always be oriented at the same angle relative to the support as at the previous or the succeeding support location. Thus, aboveground support assemblies for an elevated pipeline must have the capability of interconnecting vertical support members with a pipeline oriented at various angles to the support members.
The aboveground support assemblies must also be designed to allow for various fabrication and construction tolerances including height and spacing of the vertical support members and variations in the nominal elevation and angulation of the pipeline relative to the vertical support members. Thus provision must be made in designing the support assemblies to allow for the tolerance variations by providing adjustable interconnections between the vertical support members and any transverse interconnecting members and to provide for elevation-adjustable connections between the pipeline and the support assemblies to allow for elevation and angulation variances in the pipeline relative to the support assembly.
Provision must also be made in the aboveground support assemblies to allow for thermal contraction and expansion of the pipeline responsive to transient internal temperature changes and transient and seasonal ambient temperature variations. Although the pipeline must be rigidly affixed to the ground at spaced locations along the path of the pipeline, provision must be made at intermediate locations for longitudinal and lateral movement of the pipeline relative to the support assembly.
Moreover, in many Arctic areas, pipeline must traverse regions in which ground faults are present. Should a seismic disturbance occur, the disturbance could easily cause a shift in the ground and thus the pipeline support structures over a portion of the pipeline route. This in turn could cause the pipeline support structures for a portion of the pipeline to shift a substantial distance relative to adjacent support structures. Therefore, provision must be made in the support assemblies to allow for such movements and to prevent damage to the assemblies and the pipeline. If thermal expansion supports of the sliding type are to be employed, provision must be made to protect the pipeline and the support assemblies should the sliding connections between the pipeline and the support assembly become disengaged.